Motor-driven steering assist apparatus

ABSTRACT

In a motor-driven steering assist apparatus, a gear train transmitting a rotation of an electric motor to an output shaft comprises a single unit body surrounded by housings, and an attaching boss to a vehicle body side bracket is provided in a lower surface of the housing as seen from an axial direction of the output shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor-driven steering assistapparatus.

2. Description of the Related Art

In a motor-driven steering assist apparatus of a rough road travelingvehicle, such as a buggy vehicle or the like, as described in JapanesePatent Application Laid-open No. 2004-336565 (patent document 1), thereis a structure which is interposed between a steering wheel and a tirewheel side steering member, which assists steering force applied to thesteering wheel by a driver on the basis of torque generated by anelectric motor.

In the motor-driven steering assist apparatus in the patent document 1,a single unit body covered by first to third housings has an input shaftto which a steering wheel is connected and an output shaft to which awheel side steering member is connected. A torque sensor is providedbetween the input shaft and the output shaft. An electric motor isdriven in correspondence to a detected torque of the torque sensor. Aworm gear is coupled to a rotary shaft of the electric motor, and a wormwheel is coupled to the output shaft and is engaged with the worm gearbuilt-in. Further, an upper end portion of the input shaft and thetorque sensor are supported to the first housing. An upper end portionof the output shaft, the electric motor, the worm gear and the wormwheel are supported to the second housing. A lower end portion of theoutput shaft is supported to the third housing, and the second housingcan be attached to a vehicle body frame (a vehicle body side bracket).

In the motor-driven steering assist apparatus in the patent document 1,an attaching boss is provided at a plurality of positions in aperipheral direction of an outer periphery of the second housing, and anattaching bolt inserted and attached to the attaching boss is fastenedto a vehicle body side attaching bracket. The second housing receivesthe worm gear and the worm wheel and forms a large outer diameteritself. The attaching boss provided in the outer periphery of the secondhousing protrudes more to an outer side, the vehicle body side bracketis enlarged in size, and it is hard to avoid an interference withperipheral equipment such as an engine or the like. Further, the secondhousing receives the worm gear and forms a different outer shape, andcomplicated consideration is necessary for arranging the attaching bosswhile avoiding the worm gear receiving portion.

Further, in the motor-driven steering assist apparatus in the patentdocument 1, it is necessary that the attaching boss is provided at aplurality of positions, for example, three positions in the peripheraldirection of the outer periphery of the second housing. Three attachingbolts inserted and attached to the attaching boss are fastened, so thatit is necessary to carry out a complicated procedure.

SUMMARY OF THE INVENTION

An object of the present invention is to improve an attaching propertyto a vehicle body and to achieve a compact size and weight saving, in amotor-driven steering assist apparatus.

The present invention relates to a motor-driven steering assistapparatus interposed between a steering wheel and a wheel side steeringmember, for assisting steering force which a driver applies to thesteering wheel, on the basis of a generating torque of an electricmotor. A single unit body covered by a housing has an input shaft towhich the steering wheel is connected, an output shaft to which thewheel side steering member is connected, and a torque sensor which isprovided between the input shaft and the output shaft. An electric motoris driven in correspondence to a detected torque of the torque sensor,and a gear train transmits rotation of the electric motor to the outputshaft built-in. An attaching portion to a vehicle body side bracket isprovided in a lower surface of a housing as seen from an axial directionof the output shaft.

The present invention relates to a motor-driven steering assistapparatus interposed between a steering wheel and a wheel side steeringmember, for assisting a steering force which a driver applies to thesteering wheel, on the basis of a generating torque of an electricmotor. A single unit body covered by a housing has an input shaft towhich the steering wheel is connected, and an output shaft to which thewheel side steering member is connected. A torque sensor is providedbetween the input shaft and the output shaft. An electric motor isdriven in correspondence to a detected torque of the torque sensor, anda gear train transmits rotation of the electric motor to the outputshaft built-in. An annular attaching portion surrounding the outputshaft is provided in a protruding manner in an attaching seat formed inthe lower surface of the housing as seen from an axial direction of theoutput shaft. The annular attaching portion of the housing is insertedto an attaching hole provided in a vehicle body side attaching stay. Theattaching seat of the housing is seated on a peripheral portion of theattaching hole of the vehicle body side attaching stay, and the vehiclebody side attaching stay is pinched between a nut screwed from a leadingend side of the annular attaching portion of the housing and theattaching seat.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood from the detaileddescription given below and from the accompanying drawings which shouldnot be taken to be a limitation on the invention, but are forexplanation and understanding only.

The drawings:

FIGS. 1A and 1B show a motor-driven steering assist apparatus inaccordance with an embodiment 1, in which FIG. 1A is a schematic view ofan entire structure, and FIG. 1B is a bottom elevational view of ahousing;

FIG. 2 is a front elevational view showing the motor-driven steeringassist apparatus in accordance with the embodiment 1;

FIG. 3 is a cross sectional view along a line III-III in FIG. 2;

FIG. 4 is a cross sectional view along a line IV-IV in FIG. 2;

FIG. 5 is an entire schematic view showing a motor-driven steeringassist apparatus in accordance with an embodiment 2;

FIG. 6 is a front elevational view showing the motor-driven steeringassist apparatus in accordance with the embodiment 2;

FIG. 7 is a cross sectional view along a line VII-VII in FIG. 6;

FIG. 8 is a cross sectional view along a line VIII-VIII in FIG. 6; and

FIG. 9 is a plan view showing a vehicle body side attaching stay inaccordance with the embodiment 2;

FIG. 10 is a bottom elevational view showing a third housing inaccordance with the embodiment 2; and

FIG. 11 is a plan view showing a variant of the vehicle body sideattaching stay in accordance with the embodiment 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

A motor-driven steering assist apparatus 10 may be applied to a roughroad traveling vehicle, for example, a buggy vehicle, a snowmobile andthe like. The apparatus is interposed between a steering wheel sidesteering member 1 and a tire wheel side steering member 2, as shown inFIGS. 1 and 2, and assists steering force applied to the steering wheelby a driver, on the basis of a generated torque of an electric motor 24.A steering wheel attaching member 3 is fixed to the steering wheel sidesteering member 1, and a pitman arm 4 is fixed to the wheel sidesteering member 2. The pitman arm 4 is coupled to a front wheel viaright and left tie rods.

The motor-driven steering assist apparatus 10 comprises a single unitbody 10A covered by first housing 11 (upper housing or upper cover),second housing (main housing), and third housing (lower housing or lowercover) 13, as shown in FIGS. 1 to 4. The unit body 10A has an inputshaft 21, an output shaft 22, a torque sensor 23, an electric motor 24,a worm gear 25 and a worm wheel 26 built-in.

The motor-driven steering assist apparatus 10 comprises an upper endportion of the input shaft 21 to which the steering wheel side steeringmember 1 is connected by a connecting device 1A is supported to thefirst housing 11 (FIG. 3) by the bearing 31. Upper and lower endportions of the output shaft 22 to which the tire wheel side steeringmember 2 is connected by a connecting device 2A are supported to thesecond housing 12 and the third housing 13 by upper and lower bearings32A and 32B (FIG. 3). The input shaft 21 is provided with a serration21A for connected to the connecting device 1A in an upper end outerperipheral portion. The output shaft 22 is provided with a serration 22Afor connecting to the connecting device 2A in a lower end outerperipheral portion. A torsion bar 27 is inserted in a hollow portion ofthe input shaft 21. One end of the torsion bar 27 is coupled to theinput shaft 21 by a coupling pin 27A, and the other end of the torsionbar 27 is inserted in a hollow portion of the output shaft 22 so as tobe connected by serration.

A torque sensor 23 is provided with two detecting coils 23A and 23Bsurrounding a cylindrical core 23C engaged with the input shaft 21 andthe output shaft 22, in the first housing 11, as shown in FIG. 3. Thecore 23C is provided with a vertical groove 23E engaging with a guidepin 23D of the output shaft 22 so as to be movable only in an axialdirection, and is provided with a spiral groove 23G engaging with aslider pin 23F of the input shaft 21. Accordingly, when steering torqueapplied to the steering wheel is applied to the input shaft 21, and arelative displacement in a rotation direction is generated between theinput shaft 21 and the output shaft 22 on the basis of an elastictorsional deformation of the torsion bar 27, the displacement in therotation direction of the input shaft 21 and the output shaft 22displaces the core 23C in an axial direction. An inductance of thedetecting coils 23A and 23B caused by a magnetic change around thedetecting coils 23A and 23B due to the displacement of the core 23C ischanged. In other words, when the core 23C moves close to the inputshaft 21, the inductance of the detecting coil 23A to which the core 23Cmoves close is increased, and the inductance of the detecting coil 23Bfrom which the core 23C moves apart is reduced, whereby it is possibleto detect the steering torque on the basis of the change of theinductance.

The electric motor 24 is attached and supported to the second housing 12by a mounting bolt 28, and is driven by a controller (not shown) incorrespondence to the detected torque of the torque sensor 23. A wormgear 25 is coupled to a rotation shaft 24A of the electric motor 24 by ajoint 24B, and the worm wheel 26 engaging with the worm gear 25 is fixedto the output shaft 22. The worm gear 25 is supported at both ends tothe second housing 12 by right and left bearings 41 and 42, as shown inFIG. 4. The worm wheel 26 is fixed to the output shaft 22 just below anupper bearing 32A in the output shaft 22, in an inner portion of thesecond housing 12.

In this case, the joint 24B coupling the rotation shaft 24A of theelectric motor 24 and the worm gear 25 is structured such that a torquelimiter 24C constituted by an elastic ring is interposed in a fittinggap between both the elements (FIG. 4). The torque limiter 24C keepscoupling the rotation shaft 24A and the joint 24B under normal usingtorque conditions of the motor-driven steering assist apparatus 10,allows them to slip under abnormal torque conditions, and does nottransmit the torque of the electric motor 24 to a side of the joint 24B.

Accordingly, in the motor-driven steering assist apparatus, an integralunit body 10A is structured by supporting the upper end portion of theinput shaft 21 and the torque sensor 23 to the first housing 11. Theupper end portion of the output shaft 22, the electric motor 24, theworm gear 25 and the worm wheel 26 are supported by the second housing12. The lower end portion of the output shaft 22 is supported by thethird housing 13. The first housing 11 and the second housing 12 arecoupled by the mounting bolt 14, and the second housing 12 and the thirdhousing 13 are coupled by the mounting bolt (FIG. 3). An oil seal 33 isattached in a sealing manner to an upper opening portion of the bearing31 in the first housing 11, and an oil seal 34 is attached in a sealingmanner to a lower opening portion of the bearing 32B in the thirdhousing 13 (FIG. 3).

Further, the motor-driven steering assist apparatus 10 is provided withan attaching boss 13A to the vehicle body side bracket 17 in a lowersurface of the third housing 13 as seen from an axial direction of theoutput shaft 22. The attaching boss 13A is provided at a plurality ofpositions, three positions in the present embodiment, refer to FIG. 1B,in a peripheral direction in the periphery of the bearing 32B receivingportion for the output shaft 22, in the lower surface of the thirdhousing 13. The attaching boss 13A provided in the lower surface of thethird housing 13 is received within a profile of the second housing 12as seen from the axial direction of the output shaft 22.

In the motor-driven steering assist apparatus 10, an end surface of theattaching boss 13A of the third housing 13 of the unit body 10A ismounted on the vehicle body side bracket 17, and a center portion suchas the oil seal 34 receiving portion of the third housing 13 or thelike, and the output shaft 22 are arranged in the center hole 17A of thevehicle body side bracket 17, the attaching bolt 16 inserted andattached to the vehicle body side bracket 17 from a lower side isscrewed into a thread hole of the attaching boss 13A. The third housing13 is fastened to the vehicle body side bracket 17.

In accordance with the motor-driven steering assist apparatus 10, thesteering torque applied to the steering wheel is detected by the torquesensor 23, the electric motor 24 is driven on the basis of the detectedtorque, and the torque generated by the electric motor 24 is transmittedto the output shaft 22 via the worm gear 25 and the worm wheel 26.Accordingly, the torque generated by the electric motor 24 is used as anassist force for the steering force applied to the steering wheel by thedriver.

In accordance with the present embodiment, the following operations andeffects can be achieved.

(a) Since the attaching boss 13A is provided in the lower surface of thethird housing 13, the attaching boss 13A is downsized without protrudingto the outer side in comparison with the structure that the attachingboss 13A is provided in the outer peripheries of the first to thirdhousings 11 to 13. The vehicle body side bracket 17 is not enlarged insize, and it is possible to inhibit interference with the peripheralequipment such as the engine or the like.

(b) Since the attaching boss 13A is provided in the lower surface of thethird housing 13 even if the outer shape of the second housing 12 isformed in the different shape in the receiving portion of the worm gear25, it is possible to freely arrange the position of the attaching boss13A.

(c) Although the second housing 12 receives the worm gear 25 and theworm wheel 26 and forms the large outer diameter in itself, theattaching boss 13A is provided in the lower surface of the third housing13 so as to be received within the profile of the second housing 12, andcan be downsized.

In the present invention, the gear train transmitting the rotation ofthe electric motor to the output shaft is not limited to the structureconstituted by the worm gear and the worm wheel.

Further, in the present invention, a vibration absorbing elasticmaterial may be interposed between the vehicle body side bracket and theattaching portion provided in the lower surface of the housing.

As mentioned above, in accordance with the present invention, since theattaching portion is provided in the lower surface of the housing, theattaching portion is downsized without protruding to the outer side incomparison with the structure in which the attaching portion is providedin the outer periphery of the housing. The vehicle body side bracket isnot enlarged in size, and it is possible to inhibit interference withthe peripheral equipment such as the engine or the like.

Further, in accordance with the present invention, since the attachingportion is not provided in the outer periphery of the housing but theattaching portion is provided in the lower surface of the housing evenif the outer shape of the housing forms the different shape, it ispossible to freely arrange the position of the attaching portion.

Embodiment 2

A motor-driven steering assist apparatus 110 may be applied to a roughroad traveling vehicle, for example, a buggy vehicle, a snowmobile andthe like. The apparatus is interposed between a steering wheel sidesteering member 101 and a tire wheel side steering member 102, as shownin FIGS. 5 and 6, and assists steering force applied to the steeringwheel by a driver, on the basis of generated torque of an electric motor124. A steering wheel attaching member 103 is fixed to the steeringwheel side steering member 101, and a pitman arm 104 is fixed to thewheel side steering member 102. The pitman arm 104 is coupled to a frontwheel via right and left tie rods.

The motor-driven steering assist apparatus 110 has a single unit body110A covered by first housing 111 (upper housing or upper cover), secondhousing (main housing), and third housing (lower housing or lower cover)113, as shown in FIGS. 5 to 8. The unit body 110A has an input shaft121, an output shaft 122, a torque sensor 123, an electric motor 124, aworm gear 125 and a worm wheel 126 built-in.

The motor-driven steering assist apparatus 110 is structured such thatan upper end portion of the input shaft 121 to which the steering wheelside steering member 101 is connected by a connecting device 101A issupported to the first housing 111 (FIG. 7) by the bearing 131. Upperand lower end portions of the output shaft 122 to which the tire wheelside steering member 102 is connected by a connecting device 102A aresupported to the second housing 112 and the third housing 113 by upperand lower bearings 132A and 132B (FIG. 7). The input shaft 121 isprovided with a serration 121A for connection to the connecting device101A in an upper end outer peripheral portion. The output shaft 122 isprovided with a serration 122A for connecting to the connecting device102A in a lower end outer peripheral portion. A torsion bar 127 isinserted in a hollow portion of the input shaft 121. One end of thetorsion bar 127 is coupled to the input shaft 121 by a coupling pin127A, and the other end of the torsion bar 127 is inserted in a hollowportion of the output shaft 122 so as to be connected by serration.

A torque sensor 123 is provided with two detecting coils 123A and 123Bsurrounding a cylindrical core 123C engaged with the input shaft 121 andthe output shaft 122, in the first housing 111, as shown in FIG. 7. Thecore 123C is provided with a vertical groove 123E engaging with a guidepin 123D of the output shaft 122 so as to be movable only in an axialdirection, and is provided with a spiral groove 123G engaging with aslider pin 123F of the input shaft 121. Accordingly, when steeringtorque applied to the steering wheel is applied to the input shaft 121,and relative displacement in a rotation direction is generated betweenthe input shaft 121 and the output shaft 122 on the basis of an elastictorsional deformation of the torsion bar 127, the displacement in therotation direction of the input shaft 121 and the output shaft 122displaces the core 123C in an axial direction. An inductance of thedetecting coils 123A and 123B caused by a magnetic change around thedetecting coils 123A and 123B due to the displacement of the core 123Cis changed. In other words, when the core 123C moves close to the inputshaft 121, the inductance of the detecting coil 123A to which the core123C moves close is increased, and the inductance of the detecting coil123B from which the core 123C moves apart is reduced, whereby it ispossible to detect the steering torque on the basis of the change of theinductance.

The electric motor 124 is attached and supported to the second housing112 by a mounting bolt 128, and is driven by a controller (not shown) incorrespondence to the detected torque of the torque sensor 123. A wormgear 125 is coupled to a rotation shaft 124A of the electric motor 124by a joint 124B, and the worm wheel 126 engaging with the worm gear 125is fixed to the output shaft 122. The worm gear 125 is supported at bothends to the second housing 112 by right and left bearings 141 and 142,as shown in FIG. 8. The worm wheel 126 is fixed to the output shaft 122just below an upper bearing 132A in the output shaft 122, in an innerportion of the second housing 112.

In this case, the joint 124B coupling the rotation shaft 124A of theelectric motor 124 and the worm gear 125 is structured such that atorque limiter 124C constituted by an elastic ring is interposed in afitting gap between both the elements (FIG. 8). The torque limiter 124Ckeeps coupling the rotation shaft 124A and the joint 124B under normaltorque conditions of the motor-driven steering assist apparatus 110,allows them to slip under abnormal torque conditions, and does nottransmit the torque of the electric motor 124 to a side of the joint124B.

Accordingly, in the motor-driven steering assist apparatus, an integralunit body 110A is structured by supporting the upper end portion of theinput shaft 121 and the torque sensor 123 to the first housing 111. Theupper end portion of the output shaft 122, the electric motor 124, theworm gear 125 and the worm wheel 126 are supported by the second housing112. The lower end portion of the output shaft 122 is supported by thethird housing 113. The first housing 111 and the second housing 112 arecoupled by the mounting bolt 114, and the second housing 112 and thethird housing 113 are coupled by the mounting bolt 115 (FIG. 7). An oilseal 133 is attached in a sealing manner to an upper opening portion ofthe bearing 131 in the first housing 11, and an oil seal 134 is attachedin a sealing manner to a lower opening portion of the bearing 132B inthe third housing 113 (FIG. 7).

The motor-driven steering assist apparatus 110 is structured, as shownin FIGS. 5 to 7, such that a flat-shaped attaching seat 113A is formedin the lower surface of the third housing 113 as seen from an axialdirection of the output shaft 122. A circular ring-shaped attachingportion 113B surrounding the output shaft 122 is provided in aprotruding manner in the attaching seat 113A, and a thread portion 113Cis provided from a leading end side of the outer periphery of theattaching seat 113A (FIG. 10). Further, the annular attaching portion113B of the third housing 113 is inserted to the circular attaching hole116B provided in the vehicle body side attaching stay 116. The attachingseat 113A of the third housing 113 is seated on the peripheral portion116A of the attaching hole 116B of the vehicle body side attaching stay116. The nut 117 is screwed with the thread portion 113C in the leadingend side of the annular attaching portion 113B of the third housing 113protruding from the attaching hole 116B, the vehicle body side attachingstay 116 is pinched between the nut 117 and the attaching seat 113A, andthe third housing 113 is fastened to the vehicle body side attachingstay 116.

The attaching seat 113A and the annular attaching portion 113B providedin the lower surface of the third housing 113 are received within theprofile of the second housing 112 as seen from the axial direction ofthe output shaft 122.

Further, the motor-driven steering assist apparatus 110 is provided witha locking portion 116C obtained by cutting up a part of the peripheralportion 116A of the attaching hole 116B in the vehicle body sideattaching stay 116 (FIG. 9), and is provided with a concave lockedportion 113D in a part along the peripheral direction of the annularattaching portion 113B in the attaching seat 113A of the third housing113. Further, where the attaching seat 113A of the third housing 113 isseated on the peripheral portion 116A of the attaching hole 116B of thevehicle body side attaching stay 116, the locking portion 116C and thelocked portion 113D are engaged, and the third housing 113 is preventedfrom rotating with respect to the vehicle body side attaching stay 116.

In accordance with the motor-driven steering assist apparatus 110, thesteering torque applied to the steering wheel is detected by the torquesensor 123, the electric motor 124 is driven by the detected torque, andthe torque generated by the electric motor 124 is transmitted to theoutput shaft 122 via the worm gear 125 and the worm wheel 126.Accordingly, the torque generated by the electric motor 124 can be usedas the assist force for the steering force applied to the steering wheelby the driver.

In accordance with the present embodiment, the following operations andeffects can be achieved.

(a) Since the attaching seat 113A and the annular attaching portion 113Bare provided in the lower surface of the third housing 113, theattaching seat 113A and the annular attaching portion 113B are downsizedwithout protruding to the outer side in comparison with the structurethat the attaching seat 113A and the annular attaching portion 113B areprovided in the outer peripheries of the first to third housings 111 to113. The vehicle body side attaching stay 116 is not enlarged in size,and it is possible to inhibit the interference with the peripheralequipment such as the engine or the like.

(b) Since the attaching seat 113A and the annular attaching portion 113Bare provided in the lower surface of the third housing 113 even if theouter shape of the second housing 112 is formed in the different shapein the receiving portion of the worm gear 125, it is 110 possible tosimply form the attaching seat 113A and the annular attaching portion113B.

(c) The third housing 113 is attached to the vehicle body side attachingstay 116 in accordance with the nut fastening of the single nut 117, andit is possible to save labor expenditures.

(d) It is possible to attach the third housing 113 to the vehicle bodyside attaching stay 116 while simply preventing the third housing 113from rotating, by engaging the locked portion 113D provided in the thirdhousing 113 with the locking portion 116C of the vehicle body sideattaching stay 116.

(e) Although the second housing 112 receives the worm gear 125 and theworm wheel 126 and forms the large outer diameter in itself, theattaching seat 113A and the annular attaching portion 113B are providedin the lower surface of the third housing 113 so as to be receivedwithin the profile of the second housing 112, and can be downsized.

FIG. 11 shows a variant of the vehicle body side attaching stay 116, inwhich the attaching hole 116B is structured by notching a groove-shapedopening portion 116D open to the outer side. An opening width of theopening portion 116D is larger than an outer diameter of the outputshaft 122, and is smaller than a hole diameter of the attaching hole116B.

In accordance with the variant, the opening portion 116D leaving theattaching hole 116B open to the outer side is formed in the vehicle bodyside attaching stay 116, and the opening width of the opening portion116D is made larger than the hole diameter of the output shaft 122.Accordingly, when the motor-driven steering assist apparatus 110 isassembled between the steering wheel side steering member 101 and thetire wheel side steering member 102, the output shaft 122 of themotor-driven steering assist apparatus 110 is moved in an axiallyperpendicular direction so as to pass the output shaft 122 from theopening portion 116D of the vehicle body side attaching stay 116 to thecenter portion of the attaching hole 116B. It is further moved in theaxial direction so as to insert the annular attaching portion 113B ofthe third housing 113 to the attaching hole 116B of the vehicle bodyside attaching stay 116, thereby being assembled. Further, in accordancewith an inverse procedure, where the motor-driven steering assistapparatus 110 is assembled between the steering wheel side steeringmember 101 and the tire wheel side steering member 102, the annularattaching portion 113B of the third housing 113 can be simply detachedfrom the attaching hole 116B of the vehicle body side attaching stay116. In this case, since the opening width of the opening portion 116Dof the vehicle body side attaching stay 116 is made smaller than thehole diameter of the attaching hole 116B. The annular attaching portion113B does not extend out of the opening portion 116D of the attachinghole 116B of the vehicle body side attaching stay 116, after the annularattaching portion 113B of the third housing 113 having approximately thesame outer diameter as the hole diameter of the attaching hole 116B ofthe vehicle body side attaching stay 116 is inserted to the attachinghole 116B of the vehicle body side attaching stay 116 so as to beassembled.

As mentioned above, in accordance with the present invention, since theattaching seat and the annular attaching portion are provided in thelower surface of the housing, the attaching seat and the annularattaching portion are downsized without protruding to the outer side incomparison with the structure in which the attaching portion is providedin the outer periphery of the housing. The vehicle body side attachingstay is not enlarged in size, and it is possible to inhibit interferencewith the peripheral equipment such as the engine or the like.

Further, in accordance with the present invention, even if the outershape of the housing is formed in the different shape, the attachingportion is not provided in the outer periphery of the housing, and theattaching seat and the annular attaching portion are provided in thelower surface of the housing. Accordingly, it is possible to simply formthe attaching seat and the annular attaching portion.

As heretofore explained, embodiments of the present invention have beendescribed in detail with reference to the drawings. However, thespecific configurations of the present invention are not limited to theillustrated embodiments but those having a modification of the designwithin the range of the presently claimed invention are also included inthe present invention. In the present invention, the gear traintransmitting the rotation of the electric motor to the output shaft isnot limited to the structure constituted by the worm gear and the wormwheel.

Further, in accordance with the present invention, a vibration absorbingelastic member may be interposed between the upper surface of thevehicle body side attaching stay and the attaching seat of the housing,and between the lower surface of the vehicle body side attaching stayand the nut.

Although the invention has been illustrated and described with respectto several exemplary embodiments thereof, it should be understood bythose skilled in the art that the foregoing and various other changes,omissions and additions may be made to the present invention withoutdeparting from the spirit and scope thereof. Therefore, the presentinvention should not be understood as limited to the specific embodimentset out above, but should be understood to include all possibleembodiments which can be encompassed within a scope of equivalentsthereof with respect to the features set out in the appended claims.

1. A motor-driven steering assist apparatus interposed between a steering wheel and a wheel side steering member for assisting steering force which a driver applies to the steering wheel on the basis of a generating torque of an electric motor, a single unit body covered by a housing having an input shaft to which the steering wheel is connected, an output shaft to which the wheel side steering member is connected, a torque sensor provided between the input shaft and the output shaft, an electric motor driven in correspondence to a detected torque of the torque sensor, and a gear train which transmits a rotation of the electric motor to the output shaft built-in, wherein an attaching portion to a vehicle body side bracket is provided in a lower surface of a housing as seen from an axial direction of the output shaft.
 2. A motor-driven steering assist apparatus as claimed in claim 1, the housing comprising first to third housings, the first housing supports an upper end portion of the input shaft and the torque sensor, the second housing supports an upper end portion of the output shaft, the electric motor and the gear train, the third housing supports a lower end portion of the output shaft, and the attaching portion is provided in a lower surface of the third housing.
 3. A motor-driven steering assist apparatus as claimed in claim 2, wherein the attaching portion is received within a profile of the second housing as seen from an axial direction of the output shaft.
 4. A motor-driven steering assist apparatus as claimed in claim 2, the attaching portion comprising an attaching boss provided at a plurality of positions in a peripheral direction in the periphery of a bearing receiving portion for the output shaft, in a lower surface of the third housing.
 5. A motor-driven steering assist apparatus interposed between a steering wheel and a wheel side steering member for assisting steering force which a driver applies to the steering wheel on the basis of a generating torque of an electric motor, a single unit body covered by a housing has an input shaft to which the steering wheel is connected, an output shaft to which the wheel side steering member is connected, a torque sensor provided between the input shaft and the output shaft, an electric motor driven in correspondence to a detected torque of the torque sensor, and a gear train which transmits a rotation of the electric motor to the output shaft built-in, an annular attaching portion surrounding the output shaft provided in a protruding manner in an attaching seat formed in the lower surface of the housing as seen from an axial direction of the output shaft, wherein the annular attaching portion of the housing is inserted in an attaching hole provided in a vehicle body side attaching stay, the attaching seat of the housing is seated on a peripheral portion of the attaching hole of the vehicle body side attaching stay, and the vehicle body side attaching stay is pinched between a nut screwed from a leading end side of the annular attaching portion of the housing and the attaching seat.
 6. A motor-driven steering assist apparatus as claimed in claim 5, wherein in a state in which a locking portion is provided in the vehicle body side attaching stay, a locked portion is provided in the housing, the attaching seat of the housing is seated on the peripheral portion of the attaching hole of the vehicle body side attaching stay, and the locking portion and the locked portion are engagable so as to prevent the housing from rotating.
 7. A motor-driven steering assist apparatus as claimed in claim 5, the housing comprising first to third housings, the first housing supports an upper end portion of the input shaft and the torque sensor, the second housing supports an upper end portion of the output shaft, the electric motor and the gear train, the third housing supports a lower end portion of the output shaft, and the attaching seat and the annular attaching portion are provided in a lower surface of the third housing.
 8. A motor-driven steering assist apparatus as claimed in claim 6, the housing comprising first to third housings, the first housing supports an upper end portion of the input shaft and the torque sensor, the second housing supports an upper end portion of the output shaft, the electric motor and the gear train, the third housing supports a lower end portion of the output shaft, and the attaching seat and the annular attaching portion are provided in a lower surface of the third housing.
 9. A motor-driven steering assist apparatus as claimed in claim 7, wherein the attaching seat and the annular attaching portion are received within a profile of the second housing as seen from an axial direction of the output shaft.
 10. A motor-driven steering assist apparatus as claimed in claim 8, wherein the attaching seat and the annular attaching portion are received within a profile of the second housing as seen from an axial direction of the output shaft.
 11. A motor-driven steering assist apparatus as claimed in claim 5, wherein an opening portion leaving the attaching hole open to the outer side is formed in the vehicle body side attaching stay, and an opening width of the opening portion is larger than an outer diameter of the output shaft, and smaller than a diameter of the attaching hole.
 12. A motor-driven steering assist apparatus as claimed in claim 6, wherein an opening portion leaving the attaching hole open to the outer side is formed in the vehicle body side attaching stay, and an opening width of the opening portion is larger than an outer diameter of the output shaft, and smaller than a diameter of the attaching hole.
 13. A motor-driven steering assist apparatus as claimed in claim 7, wherein an opening portion leaving the attaching hole open to the outer side is formed in the vehicle body side attaching stay, and an opening width of the opening portion is larger than an outer diameter of the output shaft, and smaller than a diameter of the attaching hole.
 14. A motor-driven steering assist apparatus as claimed in claim 8, wherein an opening portion leaving the attaching hole open to the outer side is formed in the vehicle body side attaching stay, and an opening width of the opening portion is larger than an outer diameter of the output shaft, and smaller than a diameter of the attaching hole.
 15. A motor-driven steering assist apparatus as claimed in claim 9, wherein an opening portion leaving the attaching hole open to the outer side is formed in the vehicle body side attaching stay, and an opening width of the opening portion is larger than an outer diameter of the output shaft, and smaller than a diameter of the attaching hole.
 16. A motor-driven steering assist apparatus as claimed in claim 10, wherein an opening portion leaving the attaching hole open to the outer side is formed in the vehicle body side attaching stay, and an opening width of the opening portion is larger than an outer diameter of the output shaft, and smaller than a diameter of the attaching hole.
 17. A motor-driven steering assist apparatus as claimed in claim 7, wherein the locking portion of the vehicle body side attaching stay is formed by cutting up a part of the peripheral portion of the attaching hole, and the locked portion comprises a concave locked portion provided in a part along a peripheral direction of the annular attaching portion in the attaching seat of the third housing.
 18. A motor-driven steering assist apparatus as claimed in claim 8, wherein the locking portion of the vehicle body side attaching stay is formed by cutting up a part of the peripheral portion of the attaching hole, and the locked portion comprises a concave locked portion provided in a part along a peripheral direction of the annular attaching portion in the attaching seat of the third housing. 